Brian Hulley wrote:
Robin Green wrote:
On Wed, 29 Mar 2006 12:50:02 +0100
Jon Fairbairn <[EMAIL PROTECTED]> wrote:
[snip]
1) choosing the optimal reduction strategy is undecidable
2) we shouldn't (in general) attempt to do undecidable
things automatically
[snip]
[snip]
I suggest that a Haskell program should be treated as an executable
specification. In some cases the compiler can't optimise the program
well enough, so we (by which I mean, ordinary programmers, not
compiler geeks) should be able to explicitly provide our own
optimisations, as rewrite rules (generalised ones, or specialised
ones for individual functions). Democratise the means of automated
optimisation!
This sounds good. The only thing I'm wondering is what do we actually
gain by using Haskell in the first place instead of just a strict
language? It seems that Haskell's lazyness gives a succinct but too
inefficient program which then needs extra code in the form of
rewrite rules/pragmas, or else a complete rewrite in terms of seq etc
to get it to run fast enough without space leaks...
Thinking about this some more, I realised Jon had already answered this
question in his 3rd point:
On Wed, 29 Mar 2006 12:50:02 +0100
Jon Fairbairn <[EMAIL PROTECTED]> wrote:
> 3) Separation of concerns: Pragmatic decisions about
> evaluation order should be kept separate from the
> denotational aspect of the code. By this token, seq
I wonder if there could be a really large repository of rewrite rules on the
web somewhere, with heuristics to determine various strategies for applying
them.
There would also need to be some automated way of proving correctness of
rewrite rules, so that if someone submitted a new one it would be sure not
to introduce bugs into the optimization.
In this way, the Haskell community could gradually chip away at the
undecidableness of automatically optimizing Haskell programs, because it may
turn out to be the case that most functions are members of a very small
subset of the possible Haskell functions and could thus be handled by a
finite set of rewrite rules.
Regards, Brian.
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